Contact wetter and encoder



1966 w. H. BAUMGARTNER 3,281,829

CONTACT WETTER AND ENCODER Filed Dec. 20, 196-3 2 Sheets-Sheet 1 VI Va 2 Fig. 2. 43 47 a 5 4g-/ 49 4u8 45 3 5 KEYBOARD CONTACT CODE COMPUTER ACTUATED RESISTANCE TRANSLATION INPUT INPUT CONTROL MATRIX BUFFER SWITCH MEANS MEANS INVENTOR.

WILLIAM H. BAUMGARTNER ATTORNEY.

United States Patent 3,281,829 CONTACT WETTER AND ENCODER William H. Baumgartner, Plymouth, Mich, assignor to Burroughs Corporation, Detroit, Mich, a corporation of Michigan Filed Dec. 20, 1963, Ser. No. 332,201

5 Claims. (Cl. 340347) This invention relates to switch-actuated information handling apparatus and, more particularly, to switchactuated information handling apparatus wherein electrical contact resistance control means is employed to insure that increased contact resistance will not prevent the switches from functioning properly during normal operation.

The problem of switch-contact resistance has existed for years and many attempts have been made to eliminate this problem. It has been known for some time that during the normal operation of mechanical switching means, a high resistance film or oxidation is apt to form upon the mechanical contacts which is of such high resistance as to seriously interfere with the normal transfer of the electrical signals. Early attempts to insure reliable transfer of electrical signals through switch contacts involved greatly increasing contact pressure so as to insure good electrical contact. Other attempts to solve the contact resistance problem included the forming of contacts from special materials having oxides which are either physically or chemically unstable or which have a resistance not materially different from the contact material itself.

Additional attempts to insure reliable operation of switching contacts involved the passing of a so-called contact wetting or cleaning current through the switch contacts to insure reliable operation. In the process of electrically cleaning mechanical switching contacts, a sufficiently high potential is impressed across the switch contacts to break down or puncture the resistive oxide film, thereby dissipating the resistive film and reestablishing a low resistance path through the switch contacts.

The problems associated with increased switch contact resistance are compounded when the switching contacts are utilized in a low signal voltage system. It is usually impractical to increase the contact pressure in a miniaturized low signal voltage system such as printed circuit systems. Particularly Where miniature switches or printed circuit switch contacts are utilized, increased contact pressure is undesirable as such attempts would shorten the component life through increased wear on the surfaces of the components. The use of special contact materials involves the additional cost attendant specially made items and is, for the general application, undesirable because of this increased cost.

For the above-mentioned reasons, the electrical cleaning of switching contacts is particularly well suited for insuring good electrical contact through mechanical switching means in low cost, miniaturized, electrical systems utilizing low signal voltage levels. However, the magnitude of the potential required to clean the switching contacts electrically is often a source of great concern in low signal level systems. In one representative application involving a readily obtainable standard type switch with a particular contact pressure, a cleaning potential in the order of 55 volts, has been employed to insure reliable switching operation. In other switching applications, potentials in the range of 40 to 100 volts have been employed to obtain reliable operation. Thus, the contact cleaning potential required in representative switching assembly to insure proper operation can be troublesome, particularly in a low signal level system, as the signal level may be several orders of magnitude less than the switch-cleaning potential. To be fully compatible in an electrical system, the source of contact-cleaning potential utilized to insure proper switching operation should not dictate the power ratings of the associated electronic components nor should it represent a source of high power dissipation.

Accordingly, an objection of the present invention is to provide means for preventing objectionable interference between low level output signals or potentials in a signal translating system and a high level contact cleaning potential utilized in conjunction with mechanical switching means.

A related object is to non-interferingly incorporate a relatively high potential switching contact cleaning means into a relatively low level signal translating network utilizing a mechanical switching means for controlling the output potential level of the translating network.

Another related and important object is to combine an electrical contact wetting circuit with a contact switch actuated diode code translating matrix in such manner that, in addition to their encoding function, the same diode encoding elements coact with and form a part of the electrical switch contact wetting circuit to isolate the relatively high contact wetting potential from the relatively low potential output levels of the matrix.

Another object is to combine a switch contact resistance control means with a code translating matrix in such a manner that the potential employed to maintain good electrical contact through the input switching means maintains the unselected inputs at a potential level representative of a non-selected input.

A further object is to improve circuit means for automatically developing a momentary film breakdown voltage across selected switch contacts when a high resistive film has formed thereon.

In fulfillment of one aspect of the above listed objects, applicant employs, in combination, a contact switching means, a reference potential source, asymmetric signal translating means, a source of contact-cleaning potential, and an output potential source. With the switch open, the source of contact-cleaning potential is applied to reverse bias the asymmetric signal translating means. One contact of the switching means is connected to the reference potential source and the other contact is connected to the source of contact-cleaning potential through resistive means. Thus, when the switch is selectively closed, it a high resistive film has developed on the switching contacts, a potential equal to the absolute diiference between the reference potential and the cleaning potential is applied across the contacts to break down the resistive film and thereby restore normal contact. When normal contact has been restored through the switching controls, current flows from the reference potential source through the now closed switch contacts and the series resistance to the source of contact cleaning potential, thereby dropping the contact cleaning potential across the resistor and thus applying the reference potential as the forward biasing input to the asymmetric signal translating means to switch the output potential level from that previously established by the output potential source to substantially that of the reference potential source.

In accordance with a related aspect, the invention, as applied to a diode matrix encoder device in which the inputs are selectively enabled or pulsed through selectively actuated contact switching means, contemplates the use of the diode encoding elements in a dual capacity. In addition to their normal use as encoder elements, the invention comprehends the use of the same diodes in a simple contact wetting circuit in which they serve to isolate from the encoder output a relatively high level source of contact cleaning potential always available at the contact switching means. The contact cleaning potential is of a level, compatible with the peak inverse voltage rating of .the diodes back biased thereby, to insure puncturing or rupturing of any resistive film on the switch contacts.

The above-listed objects and other aspects of the invention will be further explained in the following detailed description and illustrated in .the accompanying drawings which disclose by way of example .the principle of the invention and the preferred embodiment for applying that principle.

For a more complete under-standing of the invention, reference may be had to the drawings in which:

FIG. 1 is a schematic diagram of a single switching circuit arranged as a signal translating system in accordance with the present invention.

FIG. 2 is a schematic block diagram of data input circuitry for a computer with a code converter embodying the present invention.

FIG. 3 is a schematic circuit diagram of data conversion circuitry utilizable in the block diagram of FIG. 2.

Referring now to FIG. 1, a schematic of a switch-operated signal translating network is shown having an input terminal 11 and an output terminal 13. The signal translating network shown is of the type which is readily adaptable to form a part of a keyboard-actuated input network where it is desired to enter binary code signals into data processing equipment such as digital computers by means of a keyboard having keys which correspond to the decimal notation. By means of such keys, an operator may enter decimally coded information directly, as in entering numbers in an adding machine or calculator, with the apparatus translating automatically the input from the decimal code and providing an output in the form of coded electrical impulses in the binary code to the data processing apparatus.

The simplified schematic of the three terminal T-type network illustrated in FIG. 1 is, for example, utilizable a-s a portion of a code translation network for converting data from a first code into a second code. Information encoded in accordance with the first code would be entered by means of the switch 15 associated with a particular row conductor of a code translating matrix, and an input signal appearing thereon would be connected by the asymmetric coupling means, shown as a diode 23, to an appropriate column conductor of the translation matrix, thereby generating an output signal representative of the information in accordance with the second code. As is well known in the art, the number of such switch controlled subassemblies would be determined by the number of elements in the first code, and the number of output column conductors would be determined by the number of elements in the second code.

In FIG. 1, an input key, not shown, would be utilized to selectively control the switch 15 having a movable contact 17 and a fixed contact 19 in series with the input line. With the switch 15 normally open, the output terminal 13 is held 'by means of the output clamping network 21, hereinafter to be described, at a potential level arbitrarily defined to correspond to the binary zero. The asymmetrical coupling element 23 is back biased by means of a contact cleaning potential source 24 connected to one terminal thereof through a resistor 25. Thus, with the switch 15 open, the output terminal 13 remains at the zero signal level and is isolated from the source 24 by the back-biased diode 23.

When the key associated with the cam controlling means 27 is actuated, movable contact 17 is freed and travels into engagement with the fixed contact 19, thereby completing the input circuit. In the event that a resistive film has formed on the switching contacts, thereby appreciably increasing the resistance therebetween, a contact cleaning potential 24 is developed across the contacts of a suflicient magnitude to puncture the resistive film and thereby restore normal conductivity.

When the switch is selectively actuated, a reference potential 29, which is connected to the movable contact 17, is applied through fixed contact 19 to the input side of the asymmetrical coupling device 23. When the switch contacts are in the proper condition, the contact cleaning potential 24 becomes a sink for current flowing from the reference potential 29 through the switch contacts 17 and 19, conductor 26 and series current limiting resistor 25 to the potential source, thereby developing at the input terminal of the asymmetrical coupling device 23 the reference potential 29, which forward biases the coupling element 23 and causes the output terminal 13 toassume a potential level arbitrarily defined to correspond to the binary one.

As herein'before stated, the output terminal 13 is normally held by the clamping network 21 at a zero signal output level when the switch 15 is open. This network is comprised of a parallel arrangement of diode 31 and resistor 33 which are respectively tied to source of output clamping potential 35 and output potential source 37. Thus, an essentially square output wave-form would be generated at the output terminal 13 in response to the selective actuation of the switch 15 by an associated input key, not shown, and if the switch contacts closed at a time t and opened at some later time t the duration of the output Wave-form would be determined by the length of time the switch 15 remained closed.

The proper operation of switch 15, having movable contact 17 and fixed contact 19, isthus assured by the automatic application of a contact cleaning potential 24 across the closed switch contact members. In the event that the resistance between the closed contact members has increased, the potential source 24 applied thereacross is suflicient to puncture the resistive oxidation and thereby restore normal conductivity through the switch contacts. At the instant normal conductivity is established through the switch 15, the cleaning potential of source 24 is dropped across the series current limiting resistor 25, thereby developing at the input terminal of the coupling device 23 the reference potential 29 which forward biases the coupling device and thereby produces a potential change at the output terminal 13 indicating a binary one.

Representative values of circuit components for the schematic diagram of FIG. 1 are:

Reference potential Referring now to FIG. 2, a block diagram is shown embodying the present invention in a keyboard controlled code translating network for directly converting decimal coded input signals into binary coded signals suitable for manipulation in an electronic data processor or the like. A well-known arrangement for translating between various codes involves the use of a so-called coded translation matrix wherein a plurality of input row conductors is utilized in conjunction with a plurality of output column conductors and a plurality of appropriately disposed interconnecting means. Information coded in accordance with a first code which is to be translated into a second code is applied to the row conductors, thereby effecting through the appropriately disposed interconnecting means signal level changes on one or more of the associated output column conductors. Cross-connections between row and column conductors may involve, as is well known in the art, asymmetrical coupling devices such as diodes.

As shown in FIG. 2, information entered from a decimal-ooded, keyboard-actuated input switching means 43 is converted into binary coded signals for processing in an electronic computer or the like. Decimally coded conductors 45-1 through 45-9 interconnect the keyboardcontrolled switching means 43 and the contact resistance control means 47 in such a manner that reliable electrical operation of the switches is insured by passing, each time a switch is closed, a contact-cleaning current through the actuated switch. When good electrical contact has been established in the switching means, an input signal is developed and impressed on the associated conductors 49-1 through 49-9, thereby generating appropriate output signals from the code translation matrix 51. The code translation matrix 51, when it is selectively actuated by an input signal appearing on any of conductors 49-1 through 49-9, uniquely generates a binary coded output signal which is applied through output lines 53-1 through 53-4 to the computer input butter 55.

The combination schematic and block diagram shown in FIG. 3 illustrates one embodiment of the present invention and shows, by way of example, circuitry utilizable in the block diagram of FIG. 2. The circuitry and associated interconnections illustrate applicants invention embodied in a signal translating device which may form a part of a keyboard-actuated, signal-translating means whereby decimally coded input information is converted directly into binary coded output information to serve as the input data for computers or the like. The decimal information is serially applied by selectively depressing decimally coded keys, not shown, which actuate the mechanical switching means 63-1 through 63-9. Keyboard-controlled, switch-actuating cam means 65-1 through 65-9 are arranged to selectively control the movable contacts 67-1 through 67-9 and, when properly positioned, to permit the selected movable contact to engage is associated fixed cont-act 69-1 through 69-9, thereby introducing an input signal on the associated conductor 71-1 through 71-9. The plurality of currentlimiting resistors 73-1 through 73-9 is tied in parallel from the respective fixed contacts of the switching means to a contact cleaning potential source 75.

With the switches open, as described hereinbefore with reference to FIG. 1, the fixed contacts 69-1 through 69-9 have a negative potential applied thereto from potential source 75, and this negative potential is also applied to the row conductors 77-1 through 77-9 of the translation matrix 79. The column conductors 81-1 through 81-4 of the translation matrix 79 are selectively interconnected with the row conductors 77-1 through 77-9 by unidirectional coupling devices in a manner well known in the art to provide translation from the decimal coded input information to the binary coded output information. The coupling devices may, by way of example, be diodes 83-1 through 83-15 selectively interconnecting the decimal input lines with the four-level binary output lines in a manner to uniquely generate for each decimal input its equivalent four-level positionally coded binary output signal.

As hereinbefore explained, each output terminal 85-1 through 85-4 has associated therewith an output clamping network 87 comprising the parallel combination of a resistor 89-1 through 89-4 and a diode 91-1 through 91-4 respectively connected to an output potential source and an output clamping level source in such a manner that the output column conductors 81-1 through 81-4 are held at the zero output signal level when the input switching means 63-1 through 63-9 are in the unselected position. The representative values of circuit component and potential biasing sources discussed hereinbefore with reference to FIG. 1 are applicable to the circuitry as shown in FIG. 3. The output signals developed by the translating matrix are applied by means of output conductors 93-1 through 93-4 to an appropriate computer input butter 55.

The embodiments shown in the foregoing figures are by way of example only. As would be evident to those skilled in the art, applicants invention might well be utilized in any unidirectional signal translating apparatus which employs mechanical switching means. It is applicants intention, therefore, to be limited only as indicated by the scope of the following claims.

I claim:

1. In a circuit for transmitting an electrical signal from a selectively controlled mechanical switch having at least two contacts through a two-terminal asymmetrical coupling device, combination means for automatically electrically cleaning said contacts without interfering with said signal when said switch is selected and for back biasing said asymmetrical coupling device when said switch is not selected comprising means including a resistor for connecting a source of relatively high direct current potential to one of said contacts of said switch and to one terminal of said asymmetrical device,

means for connecting another of said contacts to a source of reference potential, and

circuit means for connecting a relatively low direct current potential source to the other terminal of said asymmetrical device.

2. In combination, asymmetrical signal translating means having input and output terminal means,

switching means having a pair of relatively movable mechanical contacts for selectively making and breaking an electric circuit in series with said input terminal means,

means for applying a source of reference potential to one of said contacts and multipurpose circuit means including a resistor for momentarily applying a source of relatively high direct current potential across said contacts to break down any contact resistance formed thereon when said switch contacts are initially closed and for back biasing said signal translating means when said switch is open.

3. In a three-terminal T-type network for applying an electrical signal through a mechanical switching means having at least two contacts disposed in series with one arm of said T-network as the input to a unidirectional current means having input and output terminal means wherein said input terminal means is in series with the other arm of said T-network, combination means for automatically electrically cleaning said contacts when said switch is selected and for back biasing said current means when said switch is unselected comprising means for applying a source of reference potential to one of said switch contacts,

means for applying a relatively low source of direct current potential to the output terminal of said current means and dual purpose circuit means including a resistor in series with the base of said T-network for directly connecting to the other of said switch contacts and to the input of said current means a source of relatively high direct current potential of sufiicient magnitude to electrically clean said switch contacts, said source of high potential being applied through said resistor to back bias said current means when said switch is unselected and across said switch contacts when said switch is first closed and thereafter said resistor acting to isolate said high potential source from said current means thereby preventing said high potential from affecting the response of said. coupling means.

4- In a multicontact, switch-controlled code translating circuit for converting information coded in accordance with a first code into a second code, combination means for noninterferingly electrically cleaning a pair of said contacts when said contacts are selected and for insuring unique translation from said first code to said second code comprising a matrix having first and second groups of coordinate conductors interconnected by appropriately disposed ductors selectively interconnected by asymmetrical coupling means, said first group of conductors each having an input terminal connected to one contact of a different one of a plurality of multiple contact switches each identified with a different one of the input terminals and having at least one other switch contact, said second group of conductors each having an output terminal at an end thereof,

means connected to the other contact of each of said contact switches and maintaining it at a reference potential level,

a source of relatively low direct current potential connected to the output terminal of each of said sec ond group of conductors,

a plurality of resistors of relatively high resistance value each having a terminal connected to the input terminal of a different one of said input conductors of said code translating matrix,

and a relatively high direct current source of potential connected in circuit with the other terminal of each asymmetrical coupling means wherein said conductors of said first group correspond in number to the elements of said first code and individually have input terminal means on one end thereof for receiving input signals upon the selective actuation of a 5 pair of said switch contacts and for applying said input signal to a predetermined group of said asymmetrical coupling means and wherein said conductors of said second group correspond in number to the elements of said second code and have output terminal means on one end thereof,

means for applying a source of reference potential to like contacts of said pairs of switch contacts,

means for applying a source of relatively low direct current potential to the output terminal means, and

multipurpose circuit means including a plurality of voltage dividers each having at least a first resistor of relatively high value in series with the contact resistance of a pair of selectively actuatable switch contacts for momentarily applying when said conof said resistors and said reference potential maintaining means to back-bias each of said asymmetrical coupling means and supply a high potential source of contact cleaning current upon the selective actuation of any of said contact switches,

said asymmetrical coupling means isolating said high potential source of cleaning current from the output of the matrix in addition to serving as the coding elements of said code translating matrix.

No references cited.

MAYNARD R. WILBUR, Primary Examiner. K. R. STEVENS, Assistant Examiner.

5. In a contact switch controlled code translating matrix having first and second groups of coordinate con- 

4. IN A MULTICONTACT, SWITCH-CONTROLLED CODE TRANSLATING CIRCUIT FOR CONVERTING INFORMATION CODED IN ACCORDANCE WITH A FIRST CODE INTO A SECOND CODE, COMBINATION MEANS FOR NONINTERFERINGLY ELECTRICALLY CLEANING A PAIR OF SAID CONTACTS WHEN SAID CONTACTS ARE SELECTED AND FOR INSURING UNIQUE TRANSLATION FROM SAID FIRST CODE TO SAID SECOND CODE COMPRISING A MATRIX HAVING FIRST AND SECOND GROUPS OF COORDINATE CONDUCTORS INTERCONNECTED BY APPROPRIATELY DISPOSED ASYMMETRICAL COUPLING MEANS WHEREIN SAID CONDUCTORS OF SAID FIRST GROUP CORRESPOND IN NUMBER TO THE ELEMENTS OF SAID FIRST CODE AND INDIVIDUALLY HAVE INPUT TERMINAL MEANS ON ONE END THEREOF FOR RECEIVING INPUT SIGNALS UPON THE SELECTIVE ACTUATION OF A PAIR OF SAID SWITCH CONTACTS AND FOR APPLYING SAID INPUT SIGNAL TO A PREDETERMINED GROUP OF SAID ASYMMETRICAL COUPLING MEANS AND WHEREIN SAID CONDUCTORS OF SAID SECOND GROUP CORRESPOND IN NUMBER TO THE ELEMENT OF SAID SECOND CODE AND HAVE OUTPUT TERMINAL MEANS ON ONE END THEREOF, MEANS FOR APPLYING A SOURCE OF REFERENCE POTENTIAL TO LIKE CONTACTS OF SAID PAIRS OF SWITCH CONTACTS, MEANS FOR APPLYING A SOURCE OF RELATIVELY LOW DIRECT CURRENT POTENTIAL TO THE OUTPUT TERMINAL MEANS, AND MULTIPURPOSE CIRCUIT MEANS INCLUDING A PLURALITY OF VOLTAGE DIVIDERS EACH HAVING AT LEAST A FIRST RESISTOR OF RELATIVELY HIGH VALUE IN SERIES WITH THE CONTACT RESISTANCE OF A PAIR OF SELECTIVELY ACTUATABLE SWITCH CONTACT FOR MOMENTARILY APPLYING WHEN SAID CONTACTS ARE SELECTED A SOURCE OF RELATIVELY HIGH DIRECTCURRENT POTENTIAL ACROSS SAID CONTACTS TO ELECTRICALLY DISSIPATE AND RESISTIVE FILM FORMED THEREON AND THEREAFTER FOR DISSIPATING ACROSS SAID FIRST RESISTOR SAID RELATIVELY HIGH DIRECT CURRENT POTENTIAL THEREBY PREVENTING HIGH POTENTIAL FROM EFFECTING THE RESPONSE TO SAID COUPLING MEANS AFTER NORMAL CONDUCTION HAS BEEN ESTABLISHED THROUGH SAID SELECTED SWITCH CONTACTS, AND FOR APPLYING WHEN SAID PAIRS OF CONTACT ARE UNSELECTED SAID SOURCE OF RELATIVELY HIGH DIRECT CURRENT POTENTIAL IS BACK BIAS SAID ASYMMETRICCAL COUPING MEANS. 